Nanoscale Heat Transfer Modeling in Solids: Data Storage and Electronic Devices

Lattice Boltzmann method (LBM), is used to examine multi-length scale, confined heat conduction phenomena in solids for which sub-continuum regime is important. This paper describes the implementation of the method and its application to cases pertinent to data storage and electronic devices. Thin solid films with internal heat generation and with temperature difference across the boundaries are used as case studies to illustrate the benefits of the LBM. We compare our results with various hierarchical equations of heat transfer such as Fourier, Cattaneo, and Boltzmann transport equations, as well as with experimental and numerical data from the literature. Our results exhibit a good agreement with other methodologies in one and two dimensions, at a much lower computational effort.

Optimization of Air Bearing Contours for Shock Performance of a Hard Disk Drive

Hard disk drives must be designed to withstand shock during operation. Large movements of the slider during shock impulse can cause reading and writing errors, track misregistration, or in extreme cases, damage to the magnetic material and loss of data. The design of the air bearing contour determines the steady state flying conditions of the slider as well as dynamic flying conditions, including shock response. In this paper a finite element model of the hard disk drive mechanical components was developed to determine the time dependent forces and moments applied to the slider during a shock event. The time dependent forces and moments are applied as external loads in a solution of the dynamic Reynolds equation to determine the slider response to a shock event. The genetic algorithm was then used to optimize the air bearing contour for optimum shock response while keeping the steady flying conditions constant. The results show substantial differences in the spacing modulation of the head/disk interface after a shock as a function of the design of the air bearing contour.

Thermal Effects and Self-Heating Time Constant for GMR Recording Heads

An understanding of the temperature of the GMR reader element used in disk drives during operating and non-operating condition is critical to optimize its performance. Self-heating and/or external heat sources will cause an increase in the temperature of the GMR sensor. In this work we concentrate on the self-heating effect due to bias current. Experiments that monitored the resistance change during very short current pulses showed that state-of-the-art GMR sensors have an extremely short time-constant that is less than 2 ns. This work is applicable to the current transients that the GMR head experiences during electrical crosstalk, electrostatic discharge and thermal asperities.

Electrochemical Tests of Corrosion of Magnetic Hard Disks With Overcoats of DLC

Two electrochemical techniques were used to investigate the corrosion of DLC coated magnetic hard disks: (1) potentiodynamic and potentiostatic anodic polarization and (2) electrochemical impedance spectroscopy. The objective was to determine the ability of DC polarization and AC polarization to detect the presence of porosity in the DLC. The results indicate that anodic polarization at high potentials (≈ +1.0V vs SCE) to cause pitting corrosion of the metal layers underneath the DLC might provide a rapid and quantitative estimate of the amount of porosity in the DLC. Measurement of the low frequency electrochemical impedance at intermediate potentials (≈ +0.5V vs SCE) appears to indicate the presence of porosity but further work is required to establish a quantitative relationship between the amount of porosity and the value of the low frequency impedance.

Thermal Stability of Z-Type Perfluoro Poly Ether Lubricant Polymers: A Combined Thermogravimetric and Temperature Programmed Desorption Study

The thermal stability of Zdol 4000, 7800 and Ztetraol perfluoropolyethers (PFPE) have been studied in both the bulk with thermogravimetric analysis (TGA) and in thin film form with temperature programmed desorption spectroscopy (TPD). The TGA results have been interpreted to yield an evaporation activation energy for both Zdol 4000 (13 kcal/mole) and Zdol 7800 (19 kcal/mole). A larger activation energy is also found for all three samples investigated that is consistent with polymer decomposition (22, 27 and 21 kcal/mole respectively). The TPD threshold has been found to be approximately similar all three samples (∼500 K). The temperature of decomposition was also found to be similar for all three samples and was dominated by the CF2O+ mass fragment at ∼660 K. Two desorption maximums were observed for both Zdol 4000 and Ztetraol indicating the similarity in their decomposition chemistry. In contrast only one desorption peak was observed from Zdol 7800 (675 K). A CF3+ fragment was not observed in any of the TPD spectra indicating the absence an acidic decomposition path for all of the Fomblin Z polymers studied.

Measurements of Thickness, Surface Roughness and Corrosion Performance of 1-10 nm Thick CNx Films

Nitrogenated carbon (CNx) films were synthesized by using pulsed dc magnetron sputtering. When grown with substrate tilt of 45° and rotation speed of 20–25 rpm, the root-mean-square surface roughness is ∼0.3 nm when sampled over 20×20 μm2 areas, increasing to ∼0.4 nm when sampled over ∼0.05×3 cm2 using x-ray reflectivity measurements. X-ray reflectivity measurements showed that the mass density of these CNx films is ∼2.0 gm/cc, independent of film thickness from ∼1 to 10 nm, consistent with ion beam analysis. CNx films deposited with substrate tilt of 45° and rotation speed of 20–25 rpm have about 1/3 fewer corrosion spots per unit area than those without. Reducing CNx thickness from 3 to 1 nm results in marked increase in corrosion currents.

Flying Height Deviation Measurements at Ultra Low Fly Heights

The flying height tester contribution to flying height tolerance is investigated with different calibration techniques in this study. The flying attitude change in head gimbal assembly (HGA) by supplying writing current is discussed along with newly proposed methodology for feature size measurement on the air bearing slider (ABS) using a flying height tester.

Study of Transverse Flow Effects on Particle Flows and Contamination of Air Bearing Sliders

For some complex slider designs the two dimensional approximation incorporated in the Reynolds equation for determining the airflow in the air bearing is not applicable due to steps in the air bearing surface. A model that incorporates some transverse flow effects is needed to better characterize the airflow between the slider and disk for some applications. In this paper such a model is derived to better predict the paths of contamination particles entrained in the air bearing. The characteristics of airflow and particle flow within the air bearing are then studied. The analysis including the transverse effects reveals that the transverse velocity of the air is not negligible in the geometric transition regions of the slider. This transverse velocity has a significant effect on the flight path of particles, and therefore, on the particle contamination profile on slider surfaces. The assumption of adhesion of the particles upon impact with a surface is used as the contamination criteria, and it is viewed as the worst-case scenario.

Electrical Breakdown in Electrostatic Fly Control

As areal density increases and fly height decreases in hard disc drives, it becomes more difficult to achieve a reliable flying interface between the recording head and the disc. Manufacturing variations, environmental conditions and other factors can cause mechanical spacing losses. One method to compensate for these losses is to control slider clearance using electrostatic force. An attractive force between the slider and the disc can be generated by grounding the disc and applying voltage to the entire slider body or a dedicated electrode. If the applied voltage exceeds the breakdown voltage of the head-disc interface (HDI), however, the resulting current flow will cause damage to the head and disc and ultimately cause the head to crash. A series of experiments were performed on flying heads and a MEMS small-gap tester to determine the nature of the current flow and the effects of head coatings and disc lubricant on breakdown voltage. The results support field emission as the current flow mechanism. In addition, a thick diamond-like carbon (DLC) coating on the slider or electrode increases breakdown voltage and may prove to be an enabler for electrostatic fly control. In comparison, lube appears to have only a secondary effect on electrical breakdown.

Spreading Characteristics of Monolayer Lubricant Film on Surfaces With Lube Textures

In this paper, from the viewpoint of lubricant spreading, we investigate the effect of lube textures which mean a nonuniform distribution of bonding strength between lubricant molecules and the disk surface. Lube textures were formed by irradiating ultraviolet rays through a stripe-patterned mask onto a magnetic disk surface which was partially coated with one-monolayer film of perfluoropolyether. Surface characteristics of the lube textures were evaluated by surface energies ascertained from contact angle measurements. Spreading of the lubricant film was measured by scanning microellipsometry on the striped lube textures in the directions parallel and perpendicular to the stripes. The thickness-dependent diffusion coefficients extracted from the spreading profiles show that lubricant spreading in the regime of film thickness less than 0.2 nm is faster along the stripes, indicating the possibility of controlling the behavior of a lubricant film with lube textures.